Kafka transport: broken logging format strings crash subscriber and publisher threads

[klpanagi]

Description

The Kafka transport in commlib-py 0.13.1 has broken logger().info() calls that raise TypeError: not all arguments converted during string formatting. This crashes both the subscriber thread (in _on_assign) and the publisher delivery callback (_on_delivery), making Kafka pub/sub non-functional.

Affected Code

commlib/transports/kafka.py, line ~278 (_on_assign):

self.logger().info("Assignment:", partitions)

Should be:

self.logger().info("Assignment: %s", partitions)

commlib/transports/kafka.py, line ~184 (_on_delivery):

self.logger().info("Published on %s, partition", msg.topic(), f"{msg.partition()}")

Should be:

self.logger().info("Published on %s, partition %s", msg.topic(), msg.partition())

Impact

• The subscriber's _on_assign callback crashes, killing the consumer thread entirely — no messages are ever received.
• The publisher's _on_delivery callback crashes on producer.poll(0), raising an unhandled exception.

Reproduction

from commlib.transports.kafka import ConnectionParameters, Subscriber, Publisher
import time

conn = ConnectionParameters(host="localhost", port=9092)

pub = Publisher(topic="test.topic", conn_params=conn)
pub.run()
time.sleep(1)

received = []
sub = Subscriber(
    topic="test.topic",
    on_message=lambda msg: received.append(msg),
    conn_params=ConnectionParameters(host="localhost", port=9092, group="test-group"),
)
sub.run()
time.sleep(2)

pub.publish({"key": "value"})  # Triggers _on_delivery crash
time.sleep(3)
print(f"Received: {len(received)}")  # Always 0

Traceback

Exception in thread Thread-1 (run_forever):
  File "commlib/transports/kafka.py", line 278, in _on_assign
    self.logger().info("Assignment:", partitions)
  File "/usr/local/lib/python3.12/logging/__init__.py", line 392, in getMessage
    msg = msg % self.args
TypeError: not all arguments converted during string formatting

Environment

• commlib-py: 0.13.1
• confluent-kafka: 2.13.2
• Python: 3.12
• Kafka: apache/kafka 3.9.0 (KRaft mode)

Suggested Fix

Replace the two broken logging calls with correct %s-style format strings, as shown above.